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The Tunny teleprinter communications network, a harbinger of today’s mobile phone net-
works, spanned Europe and North Africa. It was used for the highest-level traffic, connecting
Hitler and the army high-command in Berlin to the front-line generals. Turing hacked into the
Tunny system, building on work done by another solitary and taciturn Bletchley Park genius,
Bill Tutte. Turing’s breakthrough in 1942 yielded the first systematic method for cracking Tunny
messages: this was known simply as ‘Turingery’ (also described in Chapter 14).
Turingery was the third of Turing’s three great contributions to the war, along with designing
the bombe and unravelling U-boat Enigma. Using Turingery, Bletchley Park was able to read
the lengthy typed exchanges between Berlin and the generals commanding the armies at the
battlefronts—conversations that laid German strategy bare. ‘Turingery was our one and only
weapon against Tunny during 1942–3’, explained 93-year-old Captain Jerry Roberts, once sec-
tion leader in the ‘Testery’, one of Bletchley Park’s two Tunny-breaking units, named after its
head Ralph Tester (see Chapter 16).
Turingery was also the seed for the sophisticated Tunny-cracking algorithms incorporated in
Tommy Flowers’ Colossus, the first large-scale electronic computer (described in Chapter 14).
With the installation of the Colossi—there were nine by the end of the war—Bletchley Park
became the world’s first electronic computing facility.
Sea lion: the invasion that never was
If Hitler’s Operation Sea Lion (Seelöwe)—his planned invasion of Great Britain in 1940—had
actually been launched, troop carriers would have poured across the English Channel from
France, accompanied by fleets of supply barges loaded with tanks, artillery, and heavy machine
guns.^8 In July 1940, Bletchley Park cracked an Enigma message revealing that the invasion was
imminent.^9
During the massive attack by sea and air, thousands of gliders crammed with heavily armed
crack German soldiers would have descended onto British soil. Paratroops would also have
rained down, with swarms of dive-bombers disabling airfields and holding back a British
ground response. Once the invaders had secured a foothold—a patch of territory containing
suitable harbours and airfields—Hitler’s formidable forces would have advanced ruthlessly in
every direction until they occupied all Britain’s key cities, or so the Führer planned.
In the event, however, the Sea Lion invasion was postponed and then abandoned. But Britain’s
fate had hung by a thread. If the Royal Air Force had not proved so resilient during the summer
of 1940, if the German leader’s attention had not been wandering in the direction of Russia,
if Turing’s second bombe, whimsically named ‘Agnus Dei’ (the Lamb of God), had not been
breaking the Luftwaffe’s top-secret Enigma communications . . . then it might all have turned
out very differently.^10 When the Imperial Japanese Air Force attacked Pearl Harbor in 1941,
Roosevelt might have faced a Europe completely dominated by Emperor Hirohito’s ally, Hitler.
Cyberwar on Rommel
The tide began to turn against the German military in 1942, with the neutralization of the
North Atlantic U-boat threat and the humiliating rout of Field Marshal Rommel’s panzer army
at El Alamein in North Africa.